Magainins are small peptides found in amphibian skins that are potent broad spectrum antibiotics. We have expressed the 23 residue peptide for uniform 15N labeling. The expressed peptide was studied in lipid bilayers on glass plates. The solid-state NMR method of structure determination was applied to the oriented peptide. The 15N chemical shift anisotropy and the 15N-1H dipolar couplings were resolved and measured. The interpretation of the structure and topology reveals an amphipathic helix lying along the surface of the membrane.